To compare a commercially available electrical muscle stimulation regime with a new form of stimulation for the rehabilitation of the quadriceps in patients with patellofemoral pain syndrome. Sixteen patients (four men, 12 women) with patellofemoral pain, demonstrable quadriceps atrophy, but normal gait parameters were randomly allocated to one of two treatment groups. One group received a sequential mixed frequency stimulation pattern from a standard device. The other group received a new form of stimulation from an experimental stimulation device that contained simultaneous mixed frequency components. Outcome measures include isometric and isokinetic extension torque, muscle fatigue rate, pain, functional questionnaire, step test, knee flexion, and quadriceps cross-sectional area. Results showed significant improvements for both groups after treatment (p less than 0.05) in all outcome measures except flexion and fatigue rates, but no significant differences between the two stimulation regimes (p greater than 0.05). Both stimulators performed similarly on patients with patellofemoral pain giving significant improvements for all patients for muscle strength, pain, self-reporting function and step testing. There were no significant differences between the two types of stimulation.